1. Field of the Invention
This invention is in the field of continuously processing silicon to melt and recrystallize the same on an assembly line basis, utilizing a parting agent which significantly prevents sticking the recrystallized silicon to the carrier.
2. Description of the Prior Art
One method for the manufacture of large area silicon crystal bodies for use as solar cells employing assembly line techniques includes the steps of placing the silicon source in solid form on a carrier member, passing the same through a furnace for melting and subsequent recrystallization, the carrier member being not appreciably wettable by the molten silicon, and then removing the carrier member from the large area silicon crystal body after recrystallization.
German OS No. 28 50 805 (U.S. Pat. No. 4,305,776) discloses a method for the manufacture of plate-shaped silicon crystal bodies in a continuous, assembly line operation wherein a carrier member composed graphite is provided with holes at periodic intervals. This carrier member is brought into contact with the silicon melt and the molten silicon is crystallized on the carrier member. A graphite net with an appropriate mesh size is preferably employed, and is integrated into the silicon crystal body which forms after crystallization.
A further cost-improved method for the manufacture of plate-shaped silicon bodies for solar cells is described in German OS No. 29 27 086. The initial starting material is a silicon powder from which a foil is produced, cut to appropriate length, and then processed into self-supporting silicon plates by means of sintering at 1350.degree. to 1400.degree. C.
In a further development, described in German OS No. 30 17 914, quartz stock or quartz sand is employed as the sintering support, preferably as a plate-pressed bulk fill.
An improvement on this method is described in German Patent Application No. 33 05 933 wherein the sintered plates are melted in a horizontal heater arrangement, the silicon being melted on a carrier member composed of a net-like graphite fabric and having similar dimensions.
The problem occurring in some of the aforementioned prior art is that, due to the incorporation of a graphite net into the silicon, impurities that are present in the carrier member can be diffused into the silicon crystal lattice and deteriorate the crystal quality as well as the electrical properties of the solar cells fabricated of this material.
In order to prevent this, German Patent Application No. P 33 38 335 proposed that the silicon sintered bodies be caused to melt and crystallize in a horizontal heater arrangement on a carrier member which is not appreciably wettable by molten silicon, the carrier being predominantly composed of a quartz glass fiber fabric which is removed after the crystallization.